Earlier today, we shared an announcement from Audi saying that it will host the world debut of five new cars at the Geneva motor show, four of which we already knew about, and asked you to tell us what you think the fifth car could be.

The mystery of the fifth model has just been solved as the brand with the four-rings released information on the new A3 Sportback g-tron, which is the flex-fuel cousin of the petrol-electric hybrid A3 Sportback e-tron that will also break cover at the Swiss car show.

The g-tron is powered by a specially-developed version of the conventional A3's 1.4-liter TSI four-cylinder engine modified to run on Audi's own e-gas, regular Compressed Natural Gas (CNG) or unleaded gasoline.

Among other highlights mentioned by Audi, are the g-tron's twin tanks positioned under the luggage compartment, each of which can hold 7kg (15.4 pounds) of CNG at a maximum 200 bar pressure, while each weighs 27kg (59.5 pounds) less than a conventional diesel of gasoline tank.

Another special feature is the electronic gas pressure regulator that reduces the high pressure of the gas flowing from the cylinders down to around five to nine bar in two stages, and can automatically switch over to gasoline operation when the pressure in the tank drops under ten bar.

According to Audi, the 1.4-liter turbocharged unit develops 109hp (110PS) and 200Nm (147 lb-ft) of peak torque, regardless of the fuel used. The five-door model completes the standards sprint to 100km/h (62mph) in 11.0 seconds before it tops out at 190km/h (118mph). It consumers on average less than 3.5 kilograms per 100 km of CNG or Audi e-gas, while in gasoline mode, it emits less than 95g of CO2 per km.

"The CO2-neutral e-gas from Werlte will power 1,500 new Audi A3 Sportback g-tron vehicles 15,000 kilometers (9,320.57 miles) every year," said Audi in a statement, without getting into any more details about availability and prices.